The long-term goal of this project is to improve clinical practice and thus public health by facilitating the evidence-based construction of efficacious, adaptive preventive interventions and treatments in drug abuse. Clinicians naturally adapt the level and type of therapy according to patient outcomes such as severity, response to past therapy, risk, stressors, adherence, preference and burden. This project will develop methods for informing and enhancing this adaptive clinical practice. Adaptive interventions are composed of operationalized decision rules that input patient outcomes and output recommended alterations in intensity and/or type of therapy. The construction of adaptive interventions requires addressing questions such as, "How do we best use measures of risk and other outcomes in order to decide when a patient's therapy needs to be intensified or stepped down?". "What sequence of therapies is best for achieving maximal improvement or preventing drug dependence?" and "Should this sequence of therapies vary by patient outcomes?" This project facilitates the construction of adaptive interventions by developing the following methodological innovations. First, practical experimental designs that will yield data most useful in constructing evidence-based adaptive interventions will be developed. Second, this project will improve and evaluate analysis methods that can be used with subject data in which either or both the timing of therapeutic changes and therapy alterations are randomized. These methods can be used to construct the decision rules that comprise an adaptive intervention. Third, this project will provide methods that can be used with subject data in which the timing of therapeutic changes and therapy alterations were made according to decision rules. This third group of methods can be used to assess the utility of the decision rules comprising an implemented adaptive intervention. To ensure applicability and receive feedback this work will include collaborative research with health scientists interested in constructing adaptive interventions. The goal is to accelerate the improvement of both prevention programs and treatments. Because drug abuse and dependence are costly to society, the broader public benefits from improved prevention programs aimed at reducing drug abuse and from improved treatment for drug dependent individuals.